# Essential thrombocythaemia (ET)

Source: https://onco.cc/cancers/essential-thrombocythaemia/  
OnCo record `essential-thrombocythaemia` (Cancer). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Essential thrombocythaemia is a slow blood cancer in which the marrow makes too many platelets. Most people need only aspirin and monitoring; those at higher risk of clots take a drug to lower the platelet count, usually hydroxyurea or interferon, with anagrelide in reserve.

## Summary

Essential thrombocythaemia is a classical myeloproliferative neoplasm defined by a sustained platelet count above 450 x 10^9/L with a marrow full of large, mature megakaryocytes and no other explanation. About 60 percent carry JAK2 V617F, 20 to 25 percent a CALR mutation and 3 to 5 percent an MPL mutation; the rest are triple negative. Many people have no symptoms and are found on a routine blood count; others have headaches, visual disturbance, burning red hands and feet (erythromelalgia) or, at high platelet counts, paradoxical bleeding. Treatment is set by the IPSET-thrombosis score, which weighs age, prior clot, JAK2 status and cardiovascular risk: very low-risk patients may need nothing, low-risk patients take low-dose aspirin, and high-risk patients add cytoreduction with hydroxyurea or interferon, with anagrelide second line. The PT-1 trial showed hydroxyurea plus aspirin beats anagrelide plus aspirin on arterial clots and bleeding. Progression to myelofibrosis happens in a minority over decades and to acute leukaemia in a few percent. Bomedemstat, an LSD1 inhibitor, is in a phase 3 trial against hydroxyurea, and antibodies against mutant CALR are the first treatments aimed at the clone itself.

## Fields

- Kind: Cancer
- Last checked: 2026-09-16
- Also known as: Essential thrombocythemia; ET; Primary thrombocythaemia; Essential thrombocytosis
- Tags: essential-thrombocythaemia; mpn
- Group: haematologic
- Burden: Around one to two new cases per 100,000 people a year, with a second peak in women in their thirties; life expectancy is close to normal for most, and the risks are clots, bleeding and slow progression to myelofibrosis.
- Subtypes: JAK2 V617F-mutated (about 60 percent; higher thrombosis risk); CALR-mutated (20 to 25 percent; higher platelets, lower thrombosis risk); MPL-mutated (3 to 5 percent); Triple negative (10 to 15 percent); Prefibrotic primary myelofibrosis (a look-alike separated by marrow histology since WHO 2016)
- Biomarkers: Platelet count above 450 x 10^9/L; JAK2 V617F, CALR exon 9 and MPL W515 mutations; IPSET-thrombosis score (age over 60, prior thrombosis, JAK2 V617F, cardiovascular risk factors); Marrow histology to exclude prefibrotic myelofibrosis; Acquired von Willebrand deficiency at platelet counts above 1,000 x 10^9/L (bleeding risk with aspirin)

## Sections of this record

The page is a hub with ten sections in reading order; large sections have their own page. The same plan as JSON: https://onco.cc/api/v1/cancers/essential-thrombocythaemia/sections.json

- Overview (on the hub): The TL;DR, the family this cancer belongs to, the organ, who gets it and what the state of the art is. https://onco.cc/cancers/essential-thrombocythaemia/#overview [5 state-of-the-art points]
- Types and stages (on the hub): Anatomy, the subtypes and how they differ, how it is staged, and where advanced disease spreads. https://onco.cc/cancers/essential-thrombocythaemia/#what-it-is [5 subtypes]
- Symptoms and diagnosis (on the hub): How this cancer shows itself, how the diagnosis is confirmed, and the biomarkers clinicians test for. https://onco.cc/cancers/essential-thrombocythaemia/#finding-it [5 biomarkers]
- Treatment (on the hub): The standard of care by setting, the medicines, surgery and radiotherapy named in it, and the regimens behind them. https://onco.cc/cancers/essential-thrombocythaemia/#treating-it [5 settings, 2 decisions with options]
- Trials and papers (on the hub): Trials recruiting now, the landmark trials, the trials held by this cancer's subtypes, the key papers and what they mean, the latest literature, and the milestones year by year. https://onco.cc/cancers/essential-thrombocythaemia/#evidence [6 trials, 8 milestones]
- Biology and targets (on the hub): The molecular landscape: the targets and how often each appears, the pathways, the mechanics stages and the preclinical models. https://onco.cc/cancers/essential-thrombocythaemia/#science [7 targets]
- Countries and centres (own page): Cases by country, the UK and NHS pathway and other country lenses, the expert centres with trials on record, and the centres named on this cancer's subtypes. https://onco.cc/cancers/essential-thrombocythaemia/where-you-are/
- Decisions and support (on the hub): The decisions you may face, the aids that walk through them, the warnings on record, the first sixty days and the questions to ask. https://onco.cc/cancers/essential-thrombocythaemia/#living-with-it [20 questions, 3 red cards]
- Pipeline and open problems (own page): Everything in development, the medicines held by this cancer's subtypes, the open problems and what is being done about them, the roadmaps, and what changed on this record. https://onco.cc/cancers/essential-thrombocythaemia/coming/ [8 medicines, 6 trials, 4 open problems]
- Data (own page): Every connected record, the notes, the JSON, Markdown and RDF twins, and where the record came from and when it was checked. https://onco.cc/cancers/essential-thrombocythaemia/data/ [38 connected records]

## Standard of care

- Diagnosis: Full blood count, JAK2, CALR and MPL testing, bone marrow biopsy to confirm ET and exclude prefibrotic myelofibrosis, and exclusion of reactive causes (iron deficiency, inflammation, infection, splenectomy). ([JAK2](https://onco.cc/targets/jak2/), [JAK2 V617F](https://onco.cc/terms/jak2-v617f/), [Myeloproliferative neoplasms (PV, ET, myelofibrosis)](https://onco.cc/cancers/myeloproliferative-neoplasms/))
- Very low and low risk: Observation alone in very low risk (under 60, no clot, JAK2-negative); low-dose aspirin for low risk and for anyone with microvascular symptoms, once acquired von Willebrand deficiency is excluded at very high platelet counts. ([Aspirin](https://onco.cc/drugs/aspirin/), [Erythromelalgia](https://onco.cc/terms/erythromelalgia/))
- High risk (over 60 with JAK2 or prior clot): Cytoreduction to a platelet count under 400 x 10^9/L: hydroxyurea first line (PT-1), pegylated or ropeginterferon alfa-2b preferred under 60 and in pregnancy, anagrelide second line. ([Hydroxyurea (hydroxycarbamide)](https://onco.cc/drugs/hydroxyurea/), [PT-1 (Primary Thrombocythaemia 1)](https://onco.cc/trials/pt-1/), [Ropeginterferon alfa-2b](https://onco.cc/drugs/ropeginterferon-alfa-2b/), [Anagrelide](https://onco.cc/drugs/anagrelide/))
- Hydroxyurea resistance or intolerance: Switch to interferon or anagrelide; ruxolitinib did not beat best available therapy in MAJIC-ET but relieves symptoms. ([Anagrelide](https://onco.cc/drugs/anagrelide/), [Ruxolitinib](https://onco.cc/drugs/ruxolitinib/), [MAJIC-ET](https://onco.cc/trials/majic-et/))
- Progression to myelofibrosis: Managed as myelofibrosis: JAK inhibitors for spleen and symptoms, transplant for fit higher-risk patients. ([Myeloproliferative neoplasms (PV, ET, myelofibrosis)](https://onco.cc/cancers/myeloproliferative-neoplasms/), [Post-PV myelofibrosis (spent phase)](https://onco.cc/terms/post-pv-myelofibrosis/), [Ruxolitinib](https://onco.cc/drugs/ruxolitinib/))

## State of the art

- Most people with ET live a near-normal lifespan; the treatment question is who needs more than aspirin, and IPSET-thrombosis answers it better than platelet count alone.
- Hydroxyurea remains first line for high-risk disease because PT-1 showed fewer arterial clots and less bleeding than anagrelide.
- Interferons give molecular responses in JAK2- and CALR-mutated ET and are the choice in younger patients and pregnancy.
- Bomedemstat is the first new cytoreductive drug in a phase 3 trial against hydroxyurea in two decades.
- Mutant-CALR antibodies (INCA033989 and others) are the first treatments that target the ET clone itself, in early trials.

## Open problems

- No treatment has been shown to prevent progression to myelofibrosis or leukaemia.
- Very low-risk patients receive nothing and low-risk patients aspirin, but the evidence for aspirin in CALR-mutated low-risk disease is thin and bleeding may outweigh benefit.
- Prefibrotic myelofibrosis is still often misdiagnosed as ET, and the two need different counselling.
- Pregnancy management rests on small series; interferon is preferred but randomised data are lacking.

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Essential_thrombocythemia
- Wikipedia: https://en.wikipedia.org/wiki/Essential_thrombocythemia
- MPN Research Foundation: https://www.mpnresearchfoundation.org/essential-thrombocythemia/

## Connected records

- cancers: [Indolent and smouldering systemic mastocytosis](https://onco.cc/cancers/indolent-systemic-mastocytosis/), [Myeloproliferative neoplasms (PV, ET, myelofibrosis)](https://onco.cc/cancers/myeloproliferative-neoplasms/), [Polycythaemia vera (PV)](https://onco.cc/cancers/polycythaemia-vera/), [Primary myelofibrosis](https://onco.cc/cancers/primary-myelofibrosis/)
- terms: [Erythromelalgia](https://onco.cc/terms/erythromelalgia/), [IPSET-thrombosis score (essential thrombocythaemia)](https://onco.cc/terms/ipset-thrombosis/), [JAK2 V617F](https://onco.cc/terms/jak2-v617f/), [MPN driver mutations (JAK2 V617F, CALR, MPL) and allele burden](https://onco.cc/terms/mpn-driver-mutations/), [Post-PV myelofibrosis (spent phase)](https://onco.cc/terms/post-pv-myelofibrosis/)
- trials: [A Single-arm, Multicenter Study to Assess the Efficacy, Safety, and Tolerability of P1101 in Adults With ET](https://onco.cc/trials/nct05482971/), [A Study of Low Dose Interferon Alpha Versus Hydroxyurea in Treatment of Chronic Myeloid Neoplasms](https://onco.cc/trials/nct01387763/), [Extension Study of P1101 After Completion of Phase 2 Study in PV Patients or Phase 3 Study in ET Patients](https://onco.cc/trials/nct04655092/), [MAJIC-ET](https://onco.cc/trials/majic-et/), [PT-1 (Primary Thrombocythaemia 1)](https://onco.cc/trials/pt-1/), [Ropeginterferon Alfa-2b (P1101) vs. Anagrelide in Essential Thrombocythemia Patients With Hydroxyurea Resistance or Intolerance](https://onco.cc/trials/nct04285086/)
- drugs: [Anagrelide](https://onco.cc/drugs/anagrelide/), [Aspirin](https://onco.cc/drugs/aspirin/), [Bomedemstat](https://onco.cc/drugs/bomedemstat/), [Hydroxyurea (hydroxycarbamide)](https://onco.cc/drugs/hydroxyurea/), [INCA033989](https://onco.cc/drugs/inca033989/), [Peginterferon alfa-2b](https://onco.cc/drugs/peginterferon-alfa-2b/), [Ropeginterferon alfa-2b](https://onco.cc/drugs/ropeginterferon-alfa-2b/), [Ruxolitinib](https://onco.cc/drugs/ruxolitinib/)
- targets: [CALR](https://onco.cc/targets/calr/), [JAK2](https://onco.cc/targets/jak2/), [MPL (thrombopoietin receptor)](https://onco.cc/targets/mpl/), [PDE3A](https://onco.cc/targets/pde3a/), [PDE3B](https://onco.cc/targets/pde3b/)

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JSON: https://onco.cc/api/v1/entities/essential-thrombocythaemia.json